That one rule there makes an enchanted item superior to a rote. You get the guaranteed control of the rote and power equal to Lore + Strength and a minimum of 1 free use per session.
True, but your stress gets reset per scene unless you have to take a consequence, whereas your enchanted item is useless for the rest of the session.
Also you can prolong attack spells if needed, which might not be that great for a direct attack but could be really useful on a zone-wide attack (Like windstorm or earthquake type attack that also puts an aspect on the scene making it hard for the enemy to leave the zone). Although with any form of attack it might also be possible to do something like this:
Turn 1: Cast Water attack to try to damage some wierd dude that is running towards you looking very angry.
Turn 2: Prolong attack for 4 exchanges because it seems like it might be working.
Turn 3: Realize the enemy is a Master BCV, redirect spell into a stream of running water between you and him.
Turns 4 and 5: Run like a little girl.